Histidine-rich glycoprotein (HRGP) is a plasma protein with anti- heparin and antifibrinolytic activity that has been associated with thrombophilia in three reported families. Therefore, it may promote hypercoagulability. The objective of this project is to purify HRGP, clarify some of its structural and functional characteristics, and to develop an ELISA that will allow measurements of HRGP in a variety of clinical settings.